1. Prepare APPLE TOPPING. Heat oven to 375°F. Grease and flour 9-inch square baking pan.
2. Stir together flour, sugar, cocoa, baking powder and salt in medium bowl. Add water, shortening, egg and vanilla; beat until smooth and well blended. Spread into prepared pan. Carefully spoon APPLE TOPPING evenly over chocolate batter to within 1/2-inch from edges; DO NOT STIR.
3. Bake 35 to 40 minutes or until chocolate is set and cake-like. Serve warm or cool completely in pan on wire rack and cut into squares. Serve topped with whipped topping or ice cream, if desired. 8 to 10 servings.
APPLE TOPPING: Stir together 1 can (20 oz.) apple pie filling, 1/2 teaspoon lemon juice and 1/2 teaspoon ground cinnamon in small bowl.